Ductwork for corrosive vapor exhaust systems is used extensively in many diverse industries which utilize hazardous chemicals to process raw materials or perform manufacturing procedures. Such industries include the semiconductor, silicon wafer, plating, pharmaceutical, wastewater treatment, solar wafer, solar cell, disc drive, memory, picture tube, and flat panel production industries. Specifically, in semiconductor fabrication facilities, many different processes require ventilation of hazardous materials; for example, robotic wet benches, gas cabinets, tanks, photo resist, and dry etchers to name a few. Such ductwork also is required in many research and development laboratories, which use highly reactive, toxic, or otherwise hazardous chemicals. Such chemicals not only can put workers at risk to hazardous fumes but also are potential sources of contamination. Consequently, to be safely removed from work areas, vapors from hazardous chemicals must be exhausted through leak-proof air ducts. Duct installations can be very large, consisting of many thousands of feet of ductwork, which may be manifolded and connected to multiple exhaust fans. Forming these duct installations is a time-consuming process.
Each connection between different duct sections requires a leak-proof joint to maintain the integrity of the system. Since a leak-proof joint is required at each connection, even the smallest installation requires a considerable number of such joints. Joints must not only prevent fumes from escaping in day-to-day operations, but must also remain leak-proof after prolonged exposure to corrosive or otherwise reactive chemicals. Also, joints must not fail catastrophically in the event a flame propagates through the interior or, if exposed directly to heat such as from a fire external to the ductwork, fail mechanically or become a source of smoke particulates and other contaminants.
Typically, ducts are fabricated as sections of standard length(s), which are transported to a job site and assembled there. Duct sections may need to be connected to other duct sections, sometimes different sized or shaped ducts, to accommodate the design of the duct system or the placement of machinery that requires ventilation. One method of connecting ductwork is using a saddle tap that is bonded to the main duct.
If the exact locations of each tap are known, the taps may be attached to the duct sections during manufacturing according to specifications. If, however, the desired locations of each tap are not known, or the installation requires flexibility at the job site, the taps must be installed at the job site. On-site installation of the taps using conventional processes is an expensive and time-consuming process. Additionally, the process requires skilled labor, and if done incorrectly, the integrity of the entire system is compromised. For example, the strength of the duct near the traditional tap may be compromised or the joint may not be leak-proof.
There are several methods that have been used for on-site installation of taps to main duct sections. One process is to cut an opening or a hole in the main duct and attach a raw secondary duct. A raw duct does not have a fitting, such as a flange, on its ends. After the hole is cut, the inside edges of the main duct (where the hole was cut) must be sanded and sealed to maintain the ducts' leak-proof qualities. The labor-intensive sanding is very messy and takes time to complete and clean up. Unless mating surfaces near the hole in the main duct and the ends of the secondary duct section are first sanded or otherwise polished, the interposing sealant layer may not uniformly adhere to the surfaces. Pores could form in the hardened sealant, and fumes could leak through the pores.
After the sanding is completed, the raw end of the secondary duct is placed into the hole in the main duct. The secondary duct section must be held in place for the remainder of the installation process by another person or temporary fastening devices (e.g., clamps, stands, etc.). The installer must then make a first seal on the outside of the main duct and secondary duct using resin and fiberglass. Then a second seal must be completed on the inside of the main duct where the secondary duct has been inserted into the main duct. This process takes a long time (3-5 hours) and requires skilled labor.
A method for sealing and reinforcing a joint is to form a “lay-up” bond by tightly winding alternate layers of fine boat cloth mesh and a combination of fiberglass sheeting and coarse woven roving mesh around the joint seam. The larger the duct diameter, the more layers must be used. Each time a dry layer is wound, a “wet out” process using a resin component of the sealant must be completed. Lay-up reinforcement substantially strengthens the joint to the extent that, under tensile loading, the duct material is likely to rupture before the joint fails. While not as significant a cost driver as sanding, the lay-up method also entails considerable time and labor.
Another method of installing taps to main duct sections is using a tap with a saddle flange. The installer cuts an opening or hole in the main duct. Again, the inside edges of the main duct must be sanded and sealed. The bonding agent or adhesive is applied to the backside of the saddle flange, and the saddle flange is placed against the duct. The tap must then be held in place for the remainder of the installation, while the adhesive cures. The installer must apply a glass and resin “lay-up” on the outside of the saddle flange to hold the flange onto the outer surface of the main duct. Typically, the bond formed by the lay-up is wider than the saddle flange. An inside “lay-up” may also be required. Additionally, the installer must seal the inner edges of the main duct, where the hole was cut. Again, this process takes a long time and requires skilled labor.
Consequently, there is a need for a faster, easier and thereby more cost-effective method for maintaining duct section joint integrity. To streamline ductwork assembly, attachment of an assembly implementing the method should be simple and reliable. Embodiments of the invention address these and other problems.